Treatment with LL-37 peptide enhances antitumor effects induced by CpG oligodeoxynucleotides against ovarian cancer

There is an urgent need for innovative therapies against ovarian cancer, one of the leading causes of death from gynecological cancers in the United States. Immunotherapy employing Toll-like receptor (TLR) ligands, such as CpG oligodeoxynucleotides (CpG-ODN), may serve as a potentially promising approach in the control of ovarian tumors. The CpG-ODN requires intracellular delivery into the endosomal compartment, where it can bind to TLR9 in order to activate the immune system. In the current study, we aim to investigate whether the antimicrobial polypeptide from the cathelicidin family, LL-37, could enhance the immunostimulatory effects of CpG-ODN by increasing the uptake of CpG-ODN into the immune cells, thus enhancing the antitumor effects against ovarian cancer. We found that treatment with the combination of CpG-ODN and LL-37 generated significantly better therapeutic antitumor effects and enhanced survival in murine ovarian tumor-bearing mice compared with treatment with CpG-ODN or LL-37 alone. We also observed that treatment with the combination of CpG-ODN and LL-37 enhanced proliferation and activation of natural killer (NK) cells, but not CD4 ⁺ or CD8 ⁺ T cells, in the peritoneal cavity. Furthermore, in vivo antibody depletion experiments indicated that peritoneal NK cells played a critical role in the observed antitumor effects. Thus, our data suggest that the combination of CpG-ODN with LL-37 peptide may lead to the control of ovarian tumors through the activation of innate immunity.